How accurate is Home Assistant Green for time keeping?

Hardware
1

Scenario:

  1. There is Chrony server installed on HA Green.
  2. There is a major network or power outage, lets say about a week, and you have to rely on Chrony.
  3. Some infrastructure will still rely on NTP sync from Chrony/HA Green.
    I have here mostly entertainment devices, which will fail to work without a time source.
    (Inaccessible time servers will be re-directed by local DNS)

a) HA Green will be powered on during the time and serve as a NTP server.

b) HA Green will be offline, relying on RTC + Battery.

Mostly it will be needed just to sync NAS, PC and few client devices, but time sync is however important for some crucial services in modern smart home.

Alternative - GPS timesync?

Right now I am testing GPS with a router. Its syncing time up to 1 second accuracy, but with no PPS signal it gets rejected as a valid time source.

I guess its possible to use Grove port on HA Green to connect GPS with UART interface and sync time properly.

2

Once Chrony loose the internet connection it will become just as inaccurate as the builtin clock.
A Raspi do not even have a RTC (Real Time Clock), so if you restart it, then it will be set back to some arbitrary time.

GPS is probably the solution for such cases and there are ESP versions too for it.

HA have for a while been quite closed when it comes to time servers, but I think one of the latest releases actually opened up for used defined time servers.

1 Like
3

HA Green at least has rtc battery, however typical phone will drift 20 seconds in 5 days. Thats enough to get timeouts for internet services.

Also I am currently trying to turn Mikrotik hEX router to GPS clock server, with VK-172 gps.

It has flaws - There is no PPS pin on the router, so we are in 1 second accuracy territory. Also router does not have RTC battery either, and if GPS key is not powered from external source during reboot (solved with 10m usb extension cable with power input), it will reset with last known time, 20 seconds in the past.

So, i guess its safe to assume that most consumer electronics has 20-50 PPM accuracy, while the GPS (at least according to datasheets) is in 0,5 PPM territory.